The present invention relates to a unidirectional drive assembly of the type which is operable to rotate an output drive assembly in a single direction regardless of the forward or reverse direction of rotation of an input gear drive assembly. More particularly, the invention relates to a unidirectional drive assembly that is suitably adaptable for use in driving a mechanical watthour meter register which provides a reliable compact assembly, having highly accurate operational throughput with low manufacturing cost.
Unidirectional registers of various types have been in use for years to record power measured by electric watthour meters. These meters were initially developed to prevent attempts to defraud the utility companies by such abusive actions which might cause the meters to register an improperly low rate of power consumption. It is generally well known that a conventional induction type watthour meter can be made to rotate in a reverse direction merely by reversing the potential applied to the meter. In a conventional meter, the simplest way to perform this reversal is to simply remove the meter from its socket and re-insert it in the socket upside down. This will cause the meter to rotate in its reverse direction, causing the meter register to run down scale rather than up-scale, thus decreasing the amount of power normally registered. To prevent such misuse of registers, and a consequent economic loss to utility companies, unidirectional registers were developed which cause the meter register indicators to rotate in an up-scale direction regardless of the forward or reverse direction of rotation of the meter input gear drive assembly.
One known type of meter to prevent the aforementioned attempt to defraud the utility company utilizes a detent assembly which prevents the meter movement from rotating in the reverse direction. While this detent prevents down-scale operation of the register when the meter is inverted, the detent does not permit the meter to provide the normal billing indications.
In U.S. Pat. No. 4,039,943, issued Aug. 2, 1977, an anti-tampering watthour meter is disclosed which includes liquid contact switches which are connected between the meter voltage coil winding ends and the terminal blades of the meter. When the meter is in the inverted position, the liquid contact switches cause the voltage coil winding ends to be reversely connected between the pair of terminal blades, thus causing the meter to continue rotation in the normal direction. This patent also discloses a penalty metering arrangement in combination with the voltage reversing arrangement, which magnetically shunts the permanent magnet field of the meter damping magnet away from the watthour meter disc so that the disc is rotated at increased speed when the meter is inverted. It may be difficult however, to control the rate at which the disc rotates, and thus the rate at which the meter register is driven.
Another known anti-tampering unidirectional register in which the present invention finds use, is disclosed in U.S. Pat. No. 3,981,439, entitled "Unidirectional Drive Assembly For Gear Driven Meter Register," to Donald M. Ham and assigned to the Assignee of the present invention. In that patent, a simple low cost mechanical unidirectional drive assembly is characterized by a gear shift assembly which co-operates with an input gear assembly to drive a register indicator dial up-scale at the same rate, via an idler-gear arrangement, regardless of the direction of rotation of the meter input gear assembly.
While some of the above mentioned registers provide means to always drive the meter register up-scale and, as disclosed in U.S. Pat. No. 4,039,943, the abusive meter user may be penalized by making the meter run at a faster rate when the meter is inverted, they do not disclose a simple and economic mechanical means for accurately performing both of those functions.
It is also known in the art, that some meters, when run in the inverted position, tend to run slower than when in their normal position due to various frictional forces, such as bearing drag. Thus, unless a calibrated compensation is made for this slowdown, the utilities are still defrauded of revenues. Therefore, a need exists for a simple low cost unidirectional drive assembly capable of accurately operating a meter register to continuously read up-scale regardless of the direction of meter drive rotation and regardless of how slow the meter may tend to run in the inverted position. Further, the same need exists for such a unidirectional drive assembly which can be fabricated to penalize those who attempt to defraud the utility company in the aforedescribed manner.
It is therefore an object of the invention to provide a unidirectional drive assembly having enhanced operating capabilities.
Another object is to provide a simple low cost design unidirectional meter register drive assembly easily adaptable to operate the meter register at calibrated rates which compensate for slow down of the meter when it is in various operating positions.
A further object of the invention is to provide a unidirectional meter register with a gear shifting and calibrated gear ratio mechanism to overcome meter drag which allows the register dials to rotate in the same direction at the same rate regardless of the direction of rotation of input drive to the register and regardless of the amount of drag created by frictional forces within the meter.
Still another object is to provide an improved unidirectional drive assembly for a gear driven meter register which provides the capability of easily changing gear ratios to allow the meter register to run at one rate when the meter is driven in a forward direction and run at a faster or compensated rate when the meter is run in a reverse direction.
Additional objects and advantages of the invention will become apparent from the description which follows.